Calscience Air
Sampling Guide
A Guide to Whole Air Sampling
and Analysis
Contents
1.0
Introduction
1.1
Types of Air Samples
1.2
Types of Pollutants
1.3
Air Sampling Media
1.4
Sampling Techniques
...1
2.0
Whole Air Sampling Media
2.1
SUMMA Canisters
2.2
Silica-Lined Canisters
2.3
High-Pressure Cylinders
2.4
Tedlar Bags
..4
3.0
Things to Consider Before Sampling
3.1
Sampling Conditions
3.2
Quality Control
3.3
Target Reporting Limits
.6
4.0
Canister Sampling
4.1
Sampling Hardware
4.2
Avoiding Sampling Problems
4.3
Steps for Collecting a Grab Sample
4.4
Steps for Collecting an Integrated Sample
.8
5.0
Tedlar Bag Sampling
5.1
Sampling Equipment
5.2
Sampling Techniques
.12
6.0
Quality Control
6.1
Equipment Cleaning and Calibration
6.2
Canister Screening
6.3
Blanks
6.4
Duplicate and Split Samples
6.5
Special Reporting Requirements
13
7.0
Reporting Limits, Units, and Conversions
7.1
Reporting Units and Conversions
7.2
Reporting Limits
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1.0
Introduction
The purpose of this guide is to provide our clients with a resource for information on the collection
and analysis of whole air samples. The introduction describes different types of air samples and
sampling techniques, while the remainder of the document describes equipment and techniques
for collecting and analyzing whole air samples.
1.1
Types of Air Samples
Air samples and sampling methods are typically categorized by the air or emissions source
and/or by the type of pollutant measured. Common sources for air samples fall into five
categories: indoor air, ambient air, stationary sources, soil vapor, and mobile sources
(automobiles). Mobile source emissions are collected during the development and testing of
vehicle engines, and are outside the scope of this document.
1.1.1
Indoor Air Samples
Indoor air samples are collected in all types of living and/or workplace environments,
including industrial facilities, office buildings, and homes. Indoor air sampling is most
frequently performed for worker safety and is regulated by the Occupational Safety
and Health Administration (OSHA).
More recently, the migration of pollutants into confined indoor spaces via soil vapor
has prompted indoor air sampling. OSHA, NIOSH (National Institute of Occupational
Safety and Health) and/or EPA methods are typically referenced for collecting indoor
air samples.
1.1.2
Ambient Air Samples
Ambient samples are collected from outdoor locations, usually in the vicinity of known
or suspected sources of air pollutants at ambient temperature and humidity. Typical
locations for ambient air sampling include soil remediation sites, landfills and
manufacturing facilities.
1.1.3
Stationary Source Samples
Stationary source samples are also mainly collected outdoors, but may also occur at
indoor locations in industrial settings. Stationary source samples are collected from a
single point source of emissions, such as an exhaust stack. Typical locations for
source testing include industrial boilers, various manufacturing facilities, power
plants, and Soil Gas Vapor Extraction (SVE) and Landfill Gas (LFG) collection
systems.
Regulatory agencies that have developed methods or guidelines for ambient and
stationary source testing include EPA, CARB, DTSC, and various RWQCBs and
AQMDs.
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1.1.4
Soil Vapor Samples
Engineering investigations of possible soil and/or groundwater contamination often
include the collection and analysis of soil vapor. Analysis of these whole air samples
can occur both in the field (using mobile testing laboratories) and in fixed base
laboratories. Although analytical methods have yet to be published specifically for
soil vapor, ambient air methods are typically used.
1.2
Types of Pollutants
Air pollutants are categorized by the regulations controlling them and their chemical and
physical properties. National air standards divide air pollutants into two categories:
·
·
Criteria pollutants with established national regulatory limits: NOx, SOx, CO,
lead, ozone, and particulate matter
Hazardous Air Pollutants (HAPs), some of which have national, state or local
regulatory limits: 189 compounds including Volatile Organic Compounds (69%)
and Semi-Volatile Organic Compounds (19%)
HAPs, which are usually collected using whole air sampling, can be divided in the following
categories based on their chemical composition and physical properties:
·
·
·
1.3
Non-volatiles (metals and heavy organics, etc.) - BP>300°C
Semi-volatile Organic Compounds (SVOCs)
- BP 120-300°C
Volatile Organic Compounds (VOCs)
- BP<120°C
Air Sampling Media
This figure presents common air
sampling media for organic
compounds. Non-volatile and most
SVOCs are present in air in a form
that cannot be collected and analyzed
using whole air sampling. Sampling
for these compounds usually involves
trapping the compounds on solid
and/or liquid media, then extracting or
desorbing the media for analysis.
1,4
Figure 1: Air Sampling Media
By comparison, whole air sampling, in which air samples are collected and analyzed in the
gaseous phase, is a simpler technique. Whole air sampling is best suited for volatile, nonpolar compounds and fixed gases. However, VOCs are also collected on solid sorbent
materials (i.e., activated carbon), most often as part of industrial hygiene applications.
Some SVOCs with boiling points as high as 170°C can be collected using whole air sampling,
depending on the temperature and reactivity of the sample matrix and the sampling media.
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Generally, high-temperature, high moisture samples, such as those collected from exhaust
stacks, require special sampling considerations to prevent losses due to condensation.
Selection of whole air sampling media depends on a number of considerations. The two
most commonly used media for whole air sampling are SUMMA canisters and Tedlar bags,
both of which are discussed in greater detail in later sections.
1.4
Sampling Techniques
Collection of whole air sampling can be either active (requires a pump) or passive (no pump
required). SUMMA canisters use passive sampling, in which a vacuum is used to draw air
into the canister, whereas Tedlar bags use active sampling, in which a pump discharges
sample into the bag.
Collection of whole air samples can be taken as a grab sample (taken over short period of
time, usually < 5 minutes) or as an integrated sample (taken over a longer period of time,
usually ½ hour to 24 hours).
1.4.1
Grab Sampling
Grab sampling is used in cases when the composition of gases in the air being
sampled does not fluctuate over time, and/or when a sample needs to be taken
quickly. A grab sample provides a snapshot picture of the air or gas stream
composition at the moment of sample collection.
1.4.2
Integrated Sampling
Unlike grab sampling, which does not have a regulated flow rate, integrated sampling
requires a flow controller to regulate the rate at which sample enters the sampling
container (200 mL/minute or less, depending on the total sampling time and volume).
Integrated sampling is used when the concentration of target analytes in the air being
sampled can possibly fluctuate over time and/or a Time Weighted Average (TWA)
concentration is desired.
The following sections present more detailed information regarding whole air sampling
equipment and techniques, and the equipment and analytical services Calscience offers.
If you have questions regarding this information or need further assistance, call your
Calscience Project Manager at 1-800-888-5221.
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2.0
Whole Air Sampling Media
Calscience provides sampling media and equipment for both grab and integrated sampling,
including Tedlar bags and SUMMA canisters. In addition, specially cleaned and prescreened
canisters are available for projects where low concentrations of constituents (low ppb or ppt) need
to be quantified. The following describes the types of whole air sampling media currently offered
by Calscience.
2.1
SUMMA Canisters
SUMMA canisters are stainless steel canisters with passivated interiors that have been
electropolished to reduce the number of active sites for sample components to interact.
These canisters can be used to collect TO-14A and TO-15 analytes, as well as fixed gases
like methane, CO, CO2, O2 and N2. Canisters are cleaned and analyzed for cleanliness prior
to use, and may be cleaned and reused many times. Holding times for most analytes in
SUMMA canisters has been shown to be stable for up to 30 days2.
SUMMA canisters come in sizes ranging from
400 ml to greater than 6L. Calscience offers
1L and 6L SUMMA canisters. To the right is a
schematic of a 6L SUMMA canister. Shown
are the sample valve (1), inlet (2), and
vacuum/pressure gauge (3). Alternatively, the
gauge may be connected to a second sample
valve. The inlet of the canister can be
connected to the sample source by ¼ inch
Swagelok fittings and Teflon tubing, or left
open if sampling ambient air.
2
3
1
Figure 2: SUMMA canister
SUMMA canisters are completely evacuated prior to use. During sampling, the valve is
opened and air is drawn into the canister through the inlet until the canister pressure has
equilibrated with that of the source being sampled. The vacuum/pressure gauge is used to
monitor the canister pressure, and indicates when there is an air flow problem or when
sampling is complete.
2.2
Fused Silica-Lined SUMMA Canisters
Fused silica-lined (FSL) canisters were developed to collect reactive organic compounds not
stable in SUMMA canisters. These canisters are made the same way as SUMMA canisters,
but have been treated with an inert silica glass lining that extends the holding time for polar or
oxygenated compounds such as MTBE and sulfur-containing compounds such as
mercaptans. FSL canisters can be used to collect the same compounds as SUMMA
canisters, as well as these additional compounds.
Many of the 1L and 6L canisters provided by Calscience are silica-lined.
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2.3
High-Pressure Cylinders
A high-pressure cylinder is a thick-walled stainless
steel container with an untreated interior and a valve
at each end. These cylinders were originally
designed for the petroleum industry to collect
samples from pressurized lines. Silica-lined
cylinders are used to collect sulfur and other reactive
compounds such as formaldehyde. High pressure
cylinders are not recommended for low (sub ppm)
sample concentrations.
Figure 3: High-Pressure Cylinder
Calscience does not provide these cylinders, but can analyze samples collected in them in
some instances.
2.4
Tedlar Bags
Tedlar bags consist of two layers of Tedlar film
sealed together at the edges and a sampling valve.
Since Tedlar is inert to most substances, it can be
used to collect reactive and more stable organic
compounds as long as all sampling components
(including the valve) are non-metallic.
Figure 4: Tedlar Bags
3
The holding time for most compounds in Tedlar bags varies depending on the compound, but
is significantly less than that for canisters; typically one day or less for sulfur compounds, and
three days for other compounds. Some regulatory agencies impose their own holding time
criteria, which may be more conservative than those generally accepted by the industry.
Prior to use, VOC concentrations in Tedlar bags are generally low or not detectable (<1
ppbv). Conditioning bags prior to use by purging with nitrogen further reduces contaminants.
Once a Tedlar bag has been used, however, it cannot be reused for low concentration (subppm) sampling because the Tedlar may absorb VOCs, which can off-gas at a later time.
Tedlar bags come in a variety of sizes from <1L to 30L. Calscience stocks only 1L Tedlar
bags, but can supply other sizes upon request.
Generally speaking, Tedlar bags are less expensive and easy to handle and transport, but have a
short holding time and are fragile. SUMMA canisters have a much longer holding time and are
more rugged, but are more expensive and cannot be used for more reactive compounds such as
those containing sulfur and nitrogen unless they have been modified with an inert lining.
Finally, Tedlar bag sampling requires a pump, while SUMMA canister sampling does not.
SUMMA canisters are completely evacuated prior to use, and utilize this vacuum to draw sample
into the canister. This may be an important consideration at locations where portability or access
to power is an issue. A summary comparison of Tedlar bags and SUMMA canisters can be found
in Table 1 below.
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Table 1: Summary comparison of SUMMA Canisters vs. Tedlar Bags
SUMMA Canister
Sampling Type
Analysis Hold Time
Surface Inertness
Cleanliness
Advantages
3.0
Tedlar Bag
Passive (vacuum, no pump required) Active (pump required)
~30 days (variable depending on
analytes tested)
Excellent
Individual or Batch Certified to
<0.5ppbv; can be SIM Certified for
lower RLs
Inert, rugged, long holding time,
portable (no pump/air moving device
required)
1-3 days
Fair
VOCs may be present (low ppbv
concentrations)
Shipping ease, low cost
Things to Consider Before Sampling
3.1
Sampling Conditions
Variations in temperature, pressure and moisture content of the air being sampled have a
great effect on how samples are collected. Extremes in these conditions can compromise
sample integrity and cause problems with sample collection.
3.1.1
Pressure
Negative Pressure - If the pressure at the sampling source is significantly negative
(sample location is under vacuum), the vacuum in a SUMMA canister will not be sufficient
to draw sample into the canister. In this case, it may be necessary to use a pump to
collect the sample. If a sampling pump is required, it is important that all areas of the
pump and sampling line exposed to the sample are clean and will not react with the
sample in any way. In some instances, Tedlar bag sampling using a lung sampler may
be more appropriate (see Section 5.0).
Positive Pressure If the sampling location has a positive pressure, it may be necessary
to reduce the pressure with a valve or regulator. At no time should a SUMMA canister be
pressured to more than 40 psig.
3.1.2
Moisture
Modifications should be made for sample streams containing excess moisture (saturated
or nearly saturated). Water vapor condenses in a canister or Tedlar bag, reducing the
recovery of polar and non-polar compounds. Some test methods recommend the use of
a condensate knockout. The solution collected in the knockout is then analyzed in
addition to the whole air samples.
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3.1.3
Particulate Matter
Excess particulate in a sampling stream will plug the inlet filter of SUMMA canisters and
damage flow controllers and valves. Excess particulate should be removed prior to
sample collection. All flow controllers and restrictors supplied by Calscience come with a
particulate filter installed at the inlet (see Section 4.1.4).
3.1.4
Temperature
SUMMA canisters and Tedlar bags are designed to collect samples at near ambient
temperature and should not subjected to temperatures above 100ºC or below 0°C. In
addition, severe temperature swings will affect the flow rate of flow controllers, and
should be avoided.
3.1.5
Altitude
The altitude at which samples are collected affects the local barometric pressure, which
in turn affects gauge vacuum/pressure readings. A canister gauge that reads -29.9 Hg
at sea level will read -25 Hg at 5000 ft elevation because gauges are calibrated to read
at sea level. Generally speaking, every 1000-foot rise in elevation results in a 1 drop in
gauge pressure.
Another consequence of the lower ambient pressure at higher elevations is that the
volume of air a SUMMA canister will collect is reduced by approximately 1/5L for every
1000 ft. In other words, at 5000 ft the maximum sample volume a 6L canister can collect
is 5L. A larger volume can be collected by using a pump; however, care must be taken to
avoid contamination from the pump.
3.2
Quality Control
Some regulatory agencies (e.g. DTSC, LARWQCB) require additional canister samples be
collected for QC purposes. A description of various QC samples is provided in Section 6.0.
3.3
Target Reporting Limits
There can be variation in reporting limits (RLs) for SUMMA canister samples depending on
the final vacuum of the sample canister. Calculations for sample volumes, dilution factors,
and final reporting limits are discussed in Section 7.0.
To ensure your sampling and analysis needs are met, please discuss the specific requirements of
your sampling program with your Calscience Project Manager when ordering sampling
equipment.
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4.0
Canister Sampling
4.1
Sampling Hardware
4.1.1
Vacuum/Pressure Gauge
The gauge, which may be built into the SUMMA canister or attached using a separate
valve, is used to monitor the vacuum in the SUMMA canister before, during, and after
sampling.
The scale of the gauge ranges from -30 Hg
to, generally, 30 psig. Gauges provided by
Calscience are not designed for high accuracy
pressure measurements; rather they are used
for checking initial and final vacuums, and for
observing relative change in vacuum/pressure
readings.
4.1.2
Brass Dust Cap
Figure 5: Vacuum/Pressure Gauge
Each canister valve comes with a ¼ inch Swagelok brass cap attached to the inlet. The
cap protects the canister from loss of vacuum and contamination during transport, and
protects the threads on the valve inlet. The brass cap should be removed prior to
sampling and replaced when sampling is complete.
4.1.3
Flow controllers (Integrated Sampling Only)
4.1.3.1 Critical Orifice
A critical orifice consists of a stainless steel fitting
encompassing a ruby disk that has been precision drilled
to create an opening through which air is drawn.
4
Figure 6: Critical Orifice
The size of the opening determines how quickly air will pass through, and
therefore, the sampling rate. Upstream of the orifice is a micro-filter (see Section
4.1.4) which protects the orifice from clogging.
The flow rate through a critical orifice is relatively constant until the canister
pressure reaches about
Hg; beyond this, the flow significantly decreases.
For more uniform sampling, a diaphragm flow controller is recommended.
Calscience offers critical orifice flow controllers ranging from ½ hour to 8 hour
sampling times for a 6L SUMMA canister.
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4.1.3.2
Diaphragm Flow Controller
Diaphragm flow controllers combine a
critical orifice with a flexible diaphragm
to maintain constant sample flow over
longer periods, regardless of changes
in canister vacuum and environmental
temperature.
Critical Orifice
Diaphragm Flow Controller
Figure 7: Diaphragm Flow Controller + Critical Orifice
The flow rate for a diaphragm flow controller can be adjusted by changing the
size of the critical orifice installed in the controller. Some diaphragm controllers
can be adjusted using a set screw to establish a flow to match the required
sampling time (see Table 2 below). Calscience can provide diaphragm flow
controllers for sampling up to 24 hours in a 6L canister.
Table 2: Flow rates (standard cubic centimeters per minute)
and orifice sizes (inches) for varying sample times
Sampling Time
1L
6L
4 hr
24 hr
2 hr
12 hr
1 hr
8 hr
3 hr
1 hr
4.1.4
Flow
(sccm)
2-4
4-8
8 - 20
20 - 40
40 - 80
Orifice
size
0.0012"
0.0016"
0.0020"
0.0030"
0.0060"
Particulate Filter
Particulate Filter
Critical Orifice
Flow controllers are provided with a 2 or 7-micron
filter, which is a stainless steel frit compressed into
a Swagelok fitting. These filters are designed to
prevent the flow controller from being damaged or
plugged by particulate matter, without significantly
restricting the sample flow.
Figure 8: Particulate Filter + Critical Orifice
4.1.5
Tubing/Connecting Fittings
Teflon tubing equipped with ¼ inch Swagelok fittings is recommended for connecting
canisters to sampling ports. Plastic tubing is not recommended since it can absorb
VOCs, has severe memory effects, and is prone to cracking and breakage.
Teflon tubing is available on request.
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4.2
Avoiding Sampling Problems
Following are some guidelines for collecting samples with canisters:
·
·
·
·
4.3
Tighten fittings properly Swagelok fittings are designed to be tightened ¼-turn
past hand tight. Under or over-tightening may result in leaks in the sample train.
In addition, over-tightening may deform the fittings, which then may need to be
replaced.
Verify gauge operation Following grab sampling, check to see that the
vacuum/pressure gauge reads near zero at ambient pressure. If it does not, it
may be damaged and unusable.
Eliminate sources of contamination Return equipment between sampling
events for cleaning. Use the shortest possible sample lines and purge them
between uses. When tubing has been exposed to high concentrations in
previous sampling, do not reuse it for sampling events in which low
concentrations are expected.
Adequately purge sampling ports and tubing prior to sample collection. Ambient
air may be introduced into stationary source samples unless sample lines are
purged prior to connecting with the canister or bag used to collect sample.
Steps for Collecting a Grab Canister Sample
Before you get to the field:
1. Make sure you have all the necessary equipment, including SUMMA canisters, gauges,
tubing/accessories (if needed), and a 9/16-inch wrench. The figure below presents
typical grab sampling equipment.
1
5
Figure 9: Air Sampling Equipment (canisters, tubing , nut & ferrule , wrench)
2. If the vacuum/pressure gauge is not already attached, attach the gauge to the valve
extending horizontally from the canister. Use a wrench to tighten ¼-turn past hand tight.
Do not over tighten.
3. Read the vacuum/pressure gauge and record the initial vacuum reading on the chain-ofcustody form. If the gauge is attached to a separate (horizontal) valve, you will need to
open the valve. The vacuum should read between -28 and -30 Hg for most applications
(see Section 3.1.5 for vacuum readings at high altitudes).
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When you are ready to sample:
4. Check the canister gauge again to see that the vacuum matches the initial reading taken
above. If it does not, there may be a leak, or the gauge may be defective.
5. Remove the brass dust cap from the top of the Summa canister.
6. If using sample tubing, attach it to the inlet of the SUMMA canister and tighten ¼-turn
past hand tight. Do not over tighten.
7. To open valve and begin sampling, turn knob on valve counterclockwise one full turn.
8. Note start time. Complete sample label attached to the canister.
At end of sampling interval:
9. Once the vacuum reaches approximately
Hg, close the Summa canister valve by
turning clockwise until snug. Do not over tighten.
10. After closing the valve, record the final vacuum of the canister gauge on the chain-ofcustody form.
11. Remove tubing from the inlet to the canister, if present, and replace the brass dust cap.
12. Complete the chain-of-custody form and, after relinquishing, retain a copy.
13. Return the SUMMA canisters and vacuum/pressure gauges in the boxes or packages
provided. Tape or secure the boxes or containers and return to Calscience.
4.4
Steps for Collecting an Integrated Canister Sample
Before you get to the field:
1. Follow steps 1-3 in Section 4.3. Make sure you have all the equipment mentioned in
Section 4.3 plus flow controllers set to the desired flow rate.
When you are ready to sample:
2.
Check the pressure gauge again to see that the vacuum matches the initial reading
taken above. Remove the brass dust cap from the top of the Summa canister.
3.
Attach the flow controller assembly to the top of the canister. Tighten the nut by turning
¼-turn beyond hand tight. Do not over tighten, as this may damage the ferrule fitting
inside the flow controller and compromise the sampling effect.
4.
If using tubing, connect to the inlet of the flow controller assembly and tighten fitting
turning ¼-turn beyond hand tight. Do not over tighten.
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5.
To begin sampling, turn canister valve counter-clockwise one full turn.
6.
Note start time. Complete sample label attached to the canister.
7.
Monitor the canister vacuum periodically to ensure steady flow into the canister. If the
canister vacuum nears 0 Hg before the end of the sampling time, sampling should be
ended early to prevent bias toward the beginning of the sampling period.
At end of sampling interval:
5.0
8.
At the end of the desired sampling time (approx. -5 inches Hg on gauge), close the
canister valve by turning clockwise until snug. Do not over-tighten. If vacuum is much
lower than
Hg, consider sampling longer (collecting more sample) to avoid elevated
reporting limits.
9.
After closing the valve, record the final vacuum of the canister gauge on the chain-ofcustody form.
10.
Disconnect tubing if used and remove flow controller assembly from the canister.
Replace the brass dust cap and tighten.
11.
Complete the chain-of-custody form and, after relinquishing, retain a copy.
12.
Return the Summa canisters and flow controllers to the boxes or packages provided.
Tape or secure the boxes or containers and return to Calscience.
Tedlar Bag Sampling
5.1 Sampling Equipment
Tedlar bag samples are collected using active sampling, in which the sample is
discharged into the Tedlar bag by a pump. There are two types of samplers used for
Tedlar bag samples: in-line samplers and lung samplers.
5.1.1
In-line Sampler
With in-line sampling, air is drawn in through
a pump into the Tedlar bag at a low flow rate
(<1/2 L/min.). This technique is most often
used for indoor air sampling and is specified
by some NIOSH and OSHA methods. The
pumps used are portable and usually battery
operated.
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Figure 10: Tedlar Bag and In-line Pump
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A disadvantage of this technique is the potential for sample contamination from
the pump. If a pump has been used previously for a contaminated site, it must
be cleaned thoroughly before being reused. While flushing for an extended
period with nitrogen is usually effective, there is no guarantee the contamination
has been removed unless a QC bag is collected and analyzed.
5.1.2
Lung Sampler
The sampling pump is connected to an airtight
chamber large enough to hold the Tedlar bag.
The valve opening on the Tedlar bag is
connected to the sample source. The pump
evacuates the chamber containing the Tedlar
bag, causing sample to be drawn into the bag
from the source. With the lung sampler,
contamination issues from a pump (as
mentioned in Section 5.1.1) are eliminated.
1
Figure 11: Lung Sampler
Calscience can provide Tedlar bags but does not provide pumps or lung samplers. Low
flow in-line pumps and lung samplers can be rented or purchased from a variety of
vendors.
5.2 Sampling Techniques
Both grab and integrated samples can be collected using Tedlar bags. Integrated
samples can be collected by lowering the flow rate at which samples are collected, and/or
by using larger bags. The pumps draw sample at a constant rate, so the major problem
with sampling over longer periods is power loss or pump malfunction.
6.0
Quality Control
6.1 Equipment Cleaning and Calibration
Sampling media and equipment supplied by Calscience is either new or cleaned prior to
use. Tedlar bags and tubing are supplied new. Tedlar bags used for low concentration
sampling may be flushed and leak checked prior to use for a nominal fee.
Pressure gauges, filters, flow controllers and canisters are all heat cleaned and flushed
with air prior to use.
After cleaning and prior to being sent to the field, flow controllers are leak checked and
tested for proper flow using a calibrated flow meter.
All canisters receive either batch or individual testing (see Section 6.2) and are leak
checked prior to use.
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6.2 Canister Screening (Analysis)
One of every six canisters is analyzed by EPA TO-15 to check for contamination prior to
field use; Calscience requires the target analytes concentrations to be lower than
0.5ppbv. On request, individually screened ( certified ) canisters can be provided. SIM
screened canisters are also available for ultra low (ppt) concentration testing.
6.3 Blanks
Blanks are samples that are kept free from exposure to the sample stream, and can be
used to monitor contamination during sampling, transport, and/or storage.
6.3.1
Field Blank
A field blank is an empty canister that is filled with hydrocarbon-free air (from a
certified source) in the field and submitted with samples for analysis. Field
blanks are used to monitor field sampling and decontamination procedures. An
individually screened canister must be used for the field blank.
6.3.2
Trip Blank
A trip blank is a canister that is filled with hydrocarbon-free air prior to being
transported to the field. The canister is returned with sample canisters for
analysis.
6.4 Duplicate and Split Samples
Duplicate samples are submitted to the same laboratory for analysis to assess sampling
precision. Split samples are submitted to two separate laboratories to assess
reproducibility and consistency between laboratories.
Field duplicate and split samples are usually
collected simultaneously from a common
inlet using a Swagelok tee to split the inlet
stream. A less desirable approach is to
collect duplicates and splits in sequence.
4,5
6.5 Special Reporting Requirements (J Flags and TICs)
Figure 12: Split tee setup
On request, trace concentrations ( J flags ) and Tentatively Identified Compounds (TICs)
can be reported. Trace concentrations are estimated values that are below the
laboratory Reporting Limit (quantitation limit) but are greater than or equal to the Method
Detection Limit (MDL).
When TICs are requested, unidentified peaks found in the sample are tentatively
identified using a GC/MS library search. Because no standards are used, identification of
these peaks is tentative and concentrations reported are estimates.
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7.0
Reporting Limits, Units and Conversion Factors
7.1 Reporting Units and Unit Conversions
Units used for reporting analysis results are chosen based on convenience and
regulatory requirements. Most often, whole air sample concentrations are measured and
reported in units of parts per million, ppm (v/v), and parts per billion, ppb(v/v).
Sometimes ppmv and ppbv are used. The v/v indicates reporting is on a volume per
volume basis.
Regulatory agencies sometimes require that results be reported in other units, such as
mg/m3 and mg/L. Conversions to these mass-based units are not as straightforward as for
soil and water, as corrections must be made based on temperature and molecular weight
using the ideal gas law.
Extreme caution should be used in converting units for laboratory data; unit conversions
for air are the most commonly occurring error in the industry.
Following is an example of a typical conversion from ppb to mg/L at 1 atmosphere (ATM)
and 25°C, for an MTBE concentration of 100ppbv:
mg/L = ppb x g mol/L x MW x 106mg/g, where:
g mol = gram moles
MW = molecular weight (g/g mol)
1 ppbv = 1L/109 L; 100ppbv = 100L/109 L;
100L/109L x 1 g mol/24.04 L x 88.15 g/g mol x 106 mg/g = 0.366 mg/L
Most analytical results are reported at Standard Temperature and Pressure (STP).
Standard pressure is 1 ATM. Standard temperatures vary depending on the regulatory
agency; for example, EPA often uses 68°F (20°C) as standard, while OSHA uses 77°F
(25°C) as standard.
Table 3 below gives conversion factors for the most commonly used reporting units at
25°C and 1 ATM.
Table 3: Conversions for commonly used reporting units
Starting unit Conversion factor Ending unit
ppbv
*MW/24.46
ug/m3
ug/m3
*24.46/MW
ppbv
ug/L
*1000
ug/m3
ug/m3
/1000
ug/L
ppbv
/1000
ppmv
ppbv
(*MW/24.46 )/1000
ug/L
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Calscience Environmental Laboratories, Inc.
7.2 Reporting Limits
Tedlar bag samples generally do not require dilution for analysis unless the concentration
of a target analyte exceeds the calibration range. In these cases, the RLs for other
analytes not detected in the sample will be elevated.
SUMMA canisters often require dilution on receipt by the laboratory regardless of analyte
concentration. Because the pressure of a SUMMA canister sample received by the
laboratory is often slightly negative (approx. -5 Hg), dilution gas is added until a final
pressure of 5 psi is reached. The resulting dilution factor, known as pressurization factor,
must be used to calculate final sample concentrations.
The final reporting limit for a specific analyte would be calculated as:
Final RL = nRL x PF x DF, where:
nRL = normal laboratory reporting limit
PF = pressurization factor (dilution due to pressurization)
DF = dilution factor (for dilutions due to high sample concentrations)
The Pressurization Factor (PF) would be calculated as follows:
PF =
14.7 psig + AP psig
14.7[1 - ( RV / 29.9inHg )]
AP = analysis pressure
RV = vacuum of received can (in. Hg)
Table 4 below shows the relationship between the final vacuum of a canister (as received
by the laboratory) and PF, based on a final analysis pressure of 5 psig.
Table 4: Pressurization Factors, based on the received vacuum of canisters
Final Vacuum
(in. Hg)
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
PF
2.01 1.92 1.83 1.75 1.68 1.61 1.55 1.49 1.44 1.39 1.34
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Calscience Environmental Laboratories, Inc.
Table 5 below shows Calscience s typical RLs for some of the TO-14A/TO-15 analytes.
These RLs, which are presented without dilution, are periodically subject to change, so
we suggest checking with your Calscience Project Manager to verify these values prior to
testing.
3
Table 5: Reporting limits for a standard TO-15 list, in ppbv and ug/m
Note that this table does not represent the complete list of compounds Calscience can
determine. Reporting limits for many of these compounds can also be lowered
substantially by operating in SIM mode, and if SIM-certified canisters are used. To ensure
your analysis needs are met, please discuss the specific requirements of your project
with your Calscience Project Manager.
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Calscience Environmental Laboratories, Inc.
References
1. SKC Inc. <www.skcinc.com>
2. Brymer, D.A., Ogle, L.D., Jones, C.J., and Lewis, D.L. (1995) Viability of Using SUMMA
Polished Canisters for the Collection and Storage of Parts per Billion by Volume Level
Volatile Organics. Environmental Science & Technology, 30(1), 188-195.
3. Environmental Supply Company, Inc. <www.environsupply.com>
4. Restek Corporation <www.restek.com>
5. Swagelok Company <www.swagelok.com>
Additional Sources of Information
U.S. Environmental Protection Agency (EPA) <www.epa.gov>
National Institute for Occupational Safety and Health (NIOSH) <www.cdc.gov/niosh/>
Occupational Safety and Health Administration (OSHA) <www.osha.gov>
South Coast Air Quality Management District (SCAQMD) <www.aqmd.gov>
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